The phrase "insensitive to a detonator" should be understood to mean that the explosives are not initiated by a conventional detonator no. 8.
Explosives of the water-in-oil-emulsion type generally contain one or more oxidizing salts such as ammonium nitrate, an oil and/or a wax, possibly other fuels such as urea, aluminium, etc. an emulsifier, possibly stabilizers for the emulsion such as guar rubber and gas bubbles or gas in closed cells.
Explosives of the water-in-oil-emulsion type are described in U.S. Pat. No. 3,447,978. The desired sensitivity is achieved by enclosing gas bubbles in the emulsion by means of a special process. Thus a water solution of oxidizing salts is emulsified in an oil phase, after which the emulsion is cooled and air is worked in mechanically or gaseous microballoons are introduced. The emulsification necessitates the use of high-speed mixers.
U.S. Pat. Nos. 3,674,578, 3,715,247 and 3,765,964 describe how detonator-sensitive emulsions of water-in-oil can be manufactured with the help of special sensitizers.
Swedish patent application No. 77 08 851-6 describes the manufacture of detonator-sensitive water-in-oil-emulsions without special sensitizers. In accordance with this application a salt solution is first emulsified in an oil phase, after which microspheres (gas-carriers) are added. This method of manufacture requires the use of high-speed mixers.
U.S. Pat. No. 4,008,108 describes a method of chemically producing the gas bubbles necessary for stable detonation.
Mixers with low speeds are used in the manufacture of conventional explosives. It is a great advantage if these mixers can also be used for manufacturing explosives of the water-in-oil-emulsion type.
It has long been known that small particles (zero fibres) facilitate emulsification.